A conventional arc lamp and its associated parts typically include, as shown in FIGS. 1-3, a U-shaped core 2 having two upstanding legs extending into and adapted to be actuated by respective magnet coils 1, and an upper electrode 3. The core 2 and the upper electrode 3 are connected to each other by means of a spring 4' around a vertical rod 4 and having the lower end connected to the cross-piece of the U-shaped core by leaf springs 4", a zig-zag angle link 5 having a horizontal portion extending through rod 4, and a ring clutch 6 at the lower end of the link 5 for gripping the upper electrode 3.
The magnetic coils 1 move the cores up when they are supplied with the current to the electrodes, so as to cause an upward and downward movement of the upper electrode within a bushing 7' provided in the center of the closure plate 7 closing the glass enclosure L of the lamps, when the current is interrupted and restarted thereby to control the distance between the upper electrode 3 and a lower electrode 9, and thus control the arcing of the lamp.
In this conventional arrangement, the coil spring 4' and leaf spring 4" are provided for preventing the vibration of the core 2 from being transmitted to the link 5 as much as possible. However, these springs often fail to cut the transmission of the vibration, due to differences in frequencies, or due to possible resonance at a specific frequency of vibration. In such a case, the vibration is transmitted through the link to the electrode and vibrates the electrode, resulting in a fluctuation in the arc. An air damper or a dash pot 8 can be connected to the upper end of the link 5 for preventing the vibration, but does not provide a completly satisfactory damping effect, especially for lateral components of the vibration.
In addition, the upstanding legs of the core, in the two coils inconveniently tend to be swung laterally so as to swing the link 5 laterally, biasing the upper electrode 3 laterally and causing it in contact the wall of the bushing 7'. Consequently, the friction between the bushing 7' and the carbon electrode 3 increases, or the electrode 3 binds in the bushing, causing a deterioration of the control of the position of the upper electrode 3.
Further that the strength of the magnet coils 1 must be uneconomically large in order that they are able to lift the combined weight of the electrode 3, the core 2, and the link 5 and other associated members.
Another problem inherent in the conventional arrangement is that the arcing is stronger on the side of the electrodes on the opposite side of the center line thereof from the magnet coils 1, as shown in FIG. 4, resulting in fluctuating arcing and an uneven consumption of the electrodes as represented by the oblique ends 12 and 12' of the electrodes in FIG. 4. This is due to a repulsion force between the arc and magnetic lines of force produced by the magnet coils 2 as represented by the arrows 11 in FIG. 4. At the same time, since the conventional structure of the core cannot provide a good shielding effect, interference with the core is likely to occur.